1. Field of the Invention
The present invention relates to an observation apparatus and an observation method for capturing a spectral image of each color component based on a simultaneous method in order to observe an image of a subject.
2. Description of the Related Art
Conventionally, observation apparatuses have been proposed that radiate lights of plural types of wavelength band (that is, color lights of plural colors) onto a subject in order to capture a spectral image of each color component and to observe an image of the subject based on the captured spectral image of each color component. As an example of such an observation apparatus, a narrow-band-filter-equipped electronic endoscope system (Narrow Band Imaging: hereinafter, referred to as NBI) has particularly attracted attention in the field of endoscopes, in which a narrow band pass filer is used to narrow the wavelength band of an illumination light. In NBI, RGB color lights with their bands narrowed by a narrow band pass filter are sequentially radiated to a subject (for example, the inside of an organ of a subject), and a spectral image of each color component is captured based on a frame sequential method. Thus, NBI acquires an image of the subject. Such NBI was published by Sano, Yoshida, Kobayashi, et al. in the general conference of the Japan Gastroenterological Endoscopy Society held in October 2000. NBI enables an acquisition of an image with the fine structure of mucous membranes of a living body accurately extracted.
An observation apparatus, such as an image acquiring apparatus that uses the frame sequential method and is exemplified by NBI, sequentially acquires (captures) spectral images of color lights reflected from the subject every time the apparatus radiates illumination lights of color components, such as RGB, to the subject. Thus, when the observation apparatus that uses the frame sequential method acquires an image of one frame, a long exposure time (light-emitting time of illumination light) is required. Therefore, when the observation apparatus that uses the frame sequential method captures an image of a subject while moving or captures an image of a subject that is moving at high speed, the apparatus may acquire a blurred image. Also, it is difficult to increase the frame rate of the observation apparatus that uses the frame sequential method.
In addition to the frame sequential method described above, there is another imaging method for such an observation apparatus called a simultaneous method, in which spectral images are simultaneously captured. An observation apparatus that uses the simultaneous method generally has light-emitting units that emit respective color lights of plural colors, and a solid-state imaging element in which a color filter that separates a reflected light from a subject into color components, such as RGB, is formed on each pixel. The observation apparatus that uses the simultaneous method simultaneously radiates color lights, such as RGB, to a subject and simultaneously captures spectral images of the color components included in the reflected light from the subject in order to acquire an image of the subject. In the observation apparatus that uses the simultaneous method, the exposure time required to acquire an image of one frame is shorter compared with the frame sequential method. Therefore, the problem with the observation apparatus that uses the frame sequential method described above can be solved.
As an example of the observation apparatus that uses the simultaneous method, there is an electronic endoscope apparatus that performs a calculating process on a color image signal acquired by a solid-state imaging element without using a narrow band pass filter in order to generate a spectral image signal (refer to Japanese Patent Application Laid-open No. 2003-93336).